SA555 and LMC555 tH, tL measured values vs fomula

Hello,

Our customer evaluating timers SA555(Bipolar) and LMC555(CMOS).
The measured tH and tL values were not acceptable for them compared with fomula in the datasheet.

test condition
  Ta：-25 to 75 degreeC
  Vcc：5V +/-10%
　RA ： 10k, with 5% accuracy, 200ppm/degreeC
　RB ： 22k, same as above
　C ： 470pF, with 5% accuracy, 60ppm/degreeC

fomula
　tH ＝ 0.693 (RA ＋RB)C
　tL ＝ 0.693 (RB)C

measured value (value from fomula)
  LMC555CMX
    tH = 10.42us　（11.6us）
    tL = 7.17us （8.05us）
  SA555DR
    tH = 10.42us　（13.4us）
    tL = 7.17us （8.96us）

They think  it has to be considered with not only fomula, some parameters(ex. Ron, tplh and tphl and so on) are also considered.

But it seems there is no more information  in the datasheet.

Please give us any comment or advise.

Thanks and best regards,

Hiroshi